Existing night vision goggles require very high operating voltages and cost thousands of dollars. Typical night vision goggles are complex electro-optical devices that intensify existing light instead of relying on their own light source. Night vision goggles can be sensitive to a broad spectrum of light, from visible through infrared. In a typical configuration, a conventional lens, called the objective lens, captures ambient light and some near-infrared light. The gathered light is then sent to an image-intensifier tube. The tube outputs a high voltage, typically about 5,000 volts, to the tube components. The image-intensifier tube can use a photo cathode to convert the photons of light energy into electrons. As the electrons pass through the tube, more electrons can be released from atoms in the tube, multiplying the original number of electrons by a factor of thousands. One method to accomplish this multiplication is through the use of a micro channel plate (MCP). The MCP is positioned in the tube such that when the electrons from the photo cathode hit the first electrode of the MCP, they can be accelerated into the glass micro channels by high voltage (about 5,000 Volts) bursts being sent between the electrodes of the electrode pair. As electrons pass through the micro channels, they cause other electrons to be released in each channel using a process called cascaded secondary emission. These new electrons can also collide with other atoms, creating a chain reaction that can result in thousands of electrons leaving the channel where only a few entered.
The image-intensifier tube can be positioned so that at the end of the tube, the cascaded electrons hit a screen coated with phosphors. These electrons maintain their position in relation to the channel they passed through. The energy of the electrons causes the phosphors to reach an excited state and release photons. These phosphors create the green image on the screen that has come to characterize night vision. Since the electrons stay in the same alignment as the original photons, a reliable image can be produced. The green phosphor image can be viewed through another lens, called the ocular lens that allows you to magnify and focus the image. The night vision device can be connected to an electronic display, such as a monitor, or the image can be viewed directly through the ocular lens.
Recently, light up-conversion devices have attracted a great deal of research interest because of their potential applications in night vision, range finding, and security, as well as semiconductor wafer inspections. Early near infrared (NIR) up-conversion devices were mostly based on the heterojunction structure of inorganic semiconductors. These devices consist of two parts in series: one part for photodetection and another for luminescence. The up-conversion devices are mainly distinguished by the method of photodetection. However, the up-conversion efficiencies of recent devices continue to be very low. For example, one NIR-to-visible light up-conversion device that integrates a light-emitting diode (LED) with a semiconductor based photodetector has only exhibited a maximum external conversion efficiency of 0.048 (4.8%) W/W. Even a hybrid organic/inorganic up-conversion device that integrates an inorganic InGaAs/TnP photodetector with an organic light-emitting diode (OLED) only exhibits an external conversion efficiency of 0.7% W/W. In addition, current inorganic and hybrid up-conversion devices are expensive to fabricate and the processes used for fabricating these devices are not compatible with large area applications.